DESCRIPTION

These functions return a null-terminated string containing an
absolute pathname that is the current working directory of
the calling process.
The pathname is returned as the function result and via the argument
buf,
if present.

The
getcwd()
function copies an absolute pathname of the current working directory
to the array pointed to by
buf,
which is of length
size.

If the length of the absolute pathname of the current working directory,
including the terminating null byte, exceeds
size
bytes, NULL is returned, and
errno
is set to
ERANGE;
an application should check for this error, and allocate a larger
buffer if necessary.

As an extension to the POSIX.1-2001 standard, Linux (libc4, libc5, glibc)
getcwd()
allocates the buffer dynamically using
malloc(3)
if
buf
is NULL.
In this case, the allocated buffer has the length
size
unless
size
is zero, when
buf
is allocated as big as necessary.
The caller should
free(3)
the returned buffer.

get_current_dir_name()
will
malloc(3)
an array big enough to hold the absolute pathname of
the current working directory.
If the environment
variable
PWD
is set, and its value is correct, then that value will be returned.
The caller should
free(3)
the returned buffer.

getwd()
does not
malloc(3)
any memory.
The
buf
argument should be a pointer to an array at least
PATH_MAX
bytes long.
If the length of the absolute pathname of the current working directory,
including the terminating null byte, exceeds
PATH_MAX
bytes, NULL is returned, and
errno
is set to
ENAMETOOLONG.
(Note that on some systems,
PATH_MAX
may not be a compile-time constant;
furthermore, its value may depend on the file system, see
pathconf(3).)
For portability and security reasons, use of
getwd()
is deprecated.

RETURN VALUE

On success, these functions return a pointer to a string containing
the pathname of the current working directory.
In the case
getcwd()
and
getwd()
this is the same value as
buf.

On failure, these functions return NULL, and
errno
is set to indicate the error.
The contents of the array pointed to by
buf
are undefined on error.

The
size
argument is less than the length of the absolute pathname of the
working directory, including the terminating null byte.
You need to allocate a bigger array and try again.

CONFORMING TO

getcwd()
conforms to POSIX.1-2001.
Note however that POSIX.1-2001 leaves the behavior of
getcwd()
unspecified if
buf
is NULL.

getwd()
is present in POSIX.1-2001, but marked LEGACY.
POSIX.1-2008 removes the specification of
getwd().
Use
getcwd()
instead.
POSIX.1-2001
does not define any errors for
getwd().

get_current_dir_name()
is a GNU extension.

NOTES

Under Linux, the function
getcwd()
is a system call (since 2.1.92).
On older systems it would query
/proc/self/cwd.
If both system call and proc file system are missing, a
generic implementation is called.
Only in that case can
these calls fail under Linux with
EACCES.

These functions are often used to save the location of the current working
directory for the purpose of returning to it later.
Opening the current
directory (".") and calling
fchdir(2)
to return is usually a faster and more reliable alternative when sufficiently
many file descriptors are available, especially on platforms other than Linux.